Step 1: Preparation of the Illustrator file
This might seem like a "no brainer," but the correct preparation of your Illustrator file will save you a lot of hassle once you get into C4D.
Start by making a new Illustrator document. Because Cinema doesn't care what the document boundaries are, I like to use something easy and square, in this case 800 points by 800 points.
Since we're not going to be printing, hide those pesky page tiling lines by going to the View menu and selecting "Hide Page Tiling."[an error occurred while processing this directive]Now here comes the most important part....
Any time you're working in 3D, it's very important to properly orient yourself in the world. When beginning a model you want to start creating the parts at 0,0,0 on the X,Y and Z axes. Cinema 4D has the ability to read the 0,0 point of the Illustrator document ruler and position the contents of the file at 0,0,0 world space. This is crucial for constructing objects with their axis at the proper central location. It's possible to move the axis of an object anytime in the modeling process, but it's always best to start off on the right foot (or grid line).
So with that in mind, we are going to now set the Illustrator ruler to the exact center of the page. With nothing selected in the Illustrator file, go to the OBJECT menu, and select Object > Crop Marks > Make. This creates crop marks at the outer corners of the document. Now go back to the OBJECT menu and select Object > Crop Marks > Release. This command kills the crop marks and leaves a rectangle whose corners coincide with the locations of the crop marks. And because our crop marks were at the boundaries of our Illustrator page, we are now left with a rectangle that exactly matches our document.
Now turn on your smart guides by going to the VIEW menu and selecting Smart Guides. This activates a kind of heads-up display within Illustrator that tells you when your mouse is hovering over the edges or centers of an object. Then turn on your rulers by going to the VIEW menu and selecting Show Rulers. Next grab the ruler reset crosshairs from the upper left corner of the window, and move the ruler zero point to the center of our document bounding square.
In order to see where the center of the document is, you can drag grid lines to the center of your document by clicking the mouse anywhere in the top or left rulers and dragging to the center of the page. Once again, let the smart guides tell you where the center of the bounding box is.